Seward, for his entire life, had gone against the powerful families and sects by hurting their egos. So that, they could accept his challenge and then he would show that those so-called great families and top sects are not invincible and they could be defeated with ease.
He used the same tactic here and he was sure that the captain of the royal guards would not reject his challenge for the duel.
The reason was simple: the cultivators from the powerful families and the sects naturally thought they were superior to others from the same province, not to mention, a nameless cultivator from a lowly province.
Moreover, currently, there were so many cultivators looking at them and if he refused to accept the challenge, then the royal family would be the one to punish him and demote him to the lowest level of the royal guards or they might even make him a royal servant.
'I will never let that happen. Also, I will become the laughing stock of the province.'